The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor circuits.
In the past, the semiconductor industry utilized various methods and circuits for forming the error amplifier of a power supply control system such as a pulse width modulated (PWM) system. Advances in technology increased the demand for more efficient and more accurate power supply control systems. Often, systems required the ability to change the value of the output voltage of the power supply system under the control of an external control system such as a micro-computer. The external control system typically sent a signal to the power supply control system in order to change the value of the output voltage. In order to reduce decouple capacitor requirements, the control system generally had a programmable output impedance (often referred to as “droop”). One problem with these power supply controllers was accuracy. Often, when the value output voltage was changed the system had to supply extra current in order to charge the output capacitors of the system to the new desired voltage. However, the programmable output impedance caused a delay in charging the output capacitors which reduced the accuracy of the control system. Such inaccuracy and instability detrimentally affected the operation of the control system that used the output voltage of the power control system.
Accordingly, it is desirable to have a power supply controller that reduces the time required to change the output voltage from one value to a new value, and that more accurately changes the output voltage to the desired value.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action.